Name: how energy changes in chemical reactions
Uploaded: 2020-09-03T13:38:27.000Z
Duration: 2 min 27 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Chemistry

Energy

PS.Chm.7.2

Energy Basics

מדוע נתרן בצורתו המתכתית מגיב עם מים ויוצר גז מימן, בעוד שנתרן כלורי פשוט נמס? ניתן להסביר תופעה זו באמצעות בחינת הקשר בין כימיה לאנרגיה, הקרוי תרמוכימיה"כל צורות החומר קשורות באנרגיה, הניתנת למדידה בצורת חום או עבודה. שני סוגי האנרגיה המרכזיים הם אנרגיה פוטנציאלית וקינטית.אנרגיה פוטנציאלית מתארת את הכוחות הקשורים בהפרשי מיקום הפועלים על עצם. לסלע בראש גבעה יש יותר אנרגיה פוטנציאלית מאשר לסלע הנמצא למרגלות הגבעה, משום שהוא רחוק יותר ממרכז המסה של כדור הארץ. אנרגיה קינטית היא האנרגיה של עצם נע.אם סלע נדחף מראש גבעה, הוא מפסיד אנרגיה פוטנציאלית אך צובר אנרגיה קינטית בתנועתו. כך קורה גם לאטומים ולמולקולות המרכיבים את העצם. לעצם נייח עדיין יש אנרגיה קינטית משום שהאטומים מהם הוא עשוי יכולים לרטוט.סוג כזה של אנרגיה קינטית נקרא אנרגיה תרמית. לעצם יש אנרגיה קינטית רבה יותר ובעקבות זאת גם אנרגיה תרמית רבה יותר כשהאטומים שלו זזים באופן נמרץ יותר. עצם זה נחשב כחם.גם למולקולות יש אנרגיה פוטנציאלית הקרויה אנרגיה כימית, הקשורה במרחק היחסי של האלקטרונים מהגרעין. במהלך תגובה, אנרגיה כימית מומרת לצורות אחרות של אנרגיה, כמו אור, או פליטה אחרת של אנרגיה, כמו חום. כמות האנרגיה המועברת תלויה במבנה המולקולרי של המגיבים.במנורת גז, אצטילן בוער והופך לפחמן דו חמצני ומים, ומשחרר כמות גדולה של אנרגיה כאור. לעומת זאת, אם נוסיף נתרן הידרוקסיד לחומצת מימן כלורי תשתחרר כמות קטנה יותר של אנרגיה כחום. כדי לחקור שינויי אנרגיה, יקל עלינו לחלק את היקום ל"מערכת"המכילה את התהליך הנצפה ול"סביבה"בה יש את כל השאר.המערכת יכולה להיות פתוחה, במובן שגם אנרגיה וגם מסה יכולות לנוע בין המערכת והסביבה. והיא יכולה להיות סגורה, כך שתהיה רק המרת אנרגיה בינה לבין הסביבה. המערכת עשויה גם להיות מבודדת, ובה גם חומר וגם אנרגיה לא מועברים.

יסודות האנרגיה

<div style="direction:rtl">תגובות כימיות, כגון אלו המתרחשות כאשר מדליקים גפרור, כרוכות בשינויים באנרגיה וגם בחומר. שינויים כימיים והשינויים הנלווים באנרגיה הם חלקים חשובים בחיי היומיום. המקרו-נוטריאנטים במזון עוברים תגובות מטבוליות המספקות את האנרגיה לשמור על תפקוד הגוף. מגוון דלקים (בנזין, גז טבעי, פחם) נשרפים להפקת אנרגיה לתחבורה, חימום והפקת חשמל. תגובות כימיות תעשייתיות משתמשות בכמויות אדירות של אנרגיה לייצור חומרי גלם (כגון ברזל ואלומיניום). לאחר מכן משתמשים באנרגיה לייצור חומרי גלם אלה למוצרים שימושיים, כגון מכוניות, גורדי שחקים וגשרים. למעלה מ-90% מהאנרגיה המשמשת את בני האדם מגיעה במקור מהשמש. מדי יום, השמש מספקת לכדור הארץ כמעט פי 10,000 מכמות האנרגיה הדרושה כדי לספק את כל צורכי האנרגיה של העולם לאותו יום. האתגר הוא שנותר למצוא דרכים להמיר ולאגור אנרגיה סולארית נכנסת כך שניתן יהיה להשתמש בה בתגובות או בתהליכים כימיים שהם גם נוחים וגם לא מזהמים. צמחים וחיידקים רבים לוכדים אנרגיית שמש באמצעות פוטוסינתזה. בני אדם משחררים את האנרגיה האצורה בצמחים בעת שריפת עצים, פחם, נפט או מוצרים צמחיים אחרים כגון אתנול. הם גם משתמשים באנרגיה זו כדי לתדלק את גופם על ידי אכילת מזון שמגיע ישירות מצמחים. <h4>תרמוכימיה</h4> הרעיונות הבסיסיים של תחום חשוב במדע העוסק בכמות החום הנספגת או המשתחררת במהלך שינויים כימיים ופיזיקליים - נקראת תרמוכימיה. המושגים נמצאים בשימוש נרחב כמעט בכל התחומים המדעיים והטכניים. מדעני מזון משתמשים בתרמוכימיה כדי לקבוע את תכולת האנרגיה של מזונות. ביולוגים חוקרים את האנרגטיקה של אורגניזמים חיים, כמו בעירה מטבולית של סוכר לפחמן דו חמצני ומים. תעשיות הנפט, הגז והתחבורה, ספקי אנרגיה מתחדשת ורבים אחרים משתדלים למצוא שיטות טובות יותר להפקת אנרגיה לצרכים מסחריים ואישיים. מהנדסים שואפים לשפר את יעילות האנרגיה, למצוא דרכים טובות יותר לחמם ולקרר בתים, לקרר מזון ומשקאות ולעמוד בצרכי האנרגיה והקירור של המחשבים והאלקטרוניקה, בין היתר. הבנת העקרונות התרמוכימיים חיונית עבור כימאים, פיזיקאים, ביולוגים, גיאולוגים, כל סוג של מהנדס, וכמעט כל מי שלומד או עושה כל סוג של מדע. <h4>אֵנֶרְגִיָה</h4> ניתן להגדיר אנרגיה כיכולת לספק חום או לבצע עבודה. סוג אחד של עבודה (w) הוא תהליך של גרימת חומר לנוע כנגד כוח מתנגד. לדוגמה, בעת ניפוח צמיג אופניים - החומר מוזז (האוויר במשאבה) כנגד הכוח המנוגד של האוויר שכבר נמצא בצמיג. כמו חומר, אנרגיה מגיעה בסוגים שונים. סכמה אחת מסווגת את האנרגיה לשני סוגים: אנרגיה פוטנציאלית, האנרגיה שיש לאובייקט בגלל מיקומו היחסי, הרכבו או מצבו, ואנרגיה קינטית, האנרגיה שיש לאובייקט בגלל תנועתו. למים בראש מפל או סכר יש אנרגיה פוטנציאלית בגלל מיקומם; כאשר הוא זורם כלפי מטה דרך גנרטורים, יש לו אנרגיה קינטית שניתן להשתמש בה כדי לבצע עבודה ולהפיק חשמל במפעל הידרואלקטרי. לסוללה יש אנרגיה פוטנציאלית מכיוון שהכימיקלים שבתוכה יכולים לייצר חשמל שיכול לעשות עבודה. טקסט זה מותאם מ <a href="https://openstax.org/books/chemistry-2e/pages/5-1-energy-basics">OpenStax Chemistry 2e, Section 5.1: Energy Basics</a></div>

תגובות כימיות, כמו אלה המתרחשות כאשר אתם מדליקים גפרור, כרוכות בשינויים באנרגיה כמו גם בחומר.

שינויים כימיים והנלווים אליהם ...

Education

JoVE Core

כימיה

אחד

Thermochemistry

תרמוכימיה

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

how energy changes in chemical reactions

Chemical reactions change matter and energy at the same time. A match lighting is a simple example. These energy changes are part of everyday life and appear in food, fuels, and industry.

Food provides energy through metabolic reactions. The macronutrients in food break down and help keep the body functioning. Fuels such as gasoline, natural gas, and coal are burned to produce energy for transportation, heating, and electricity generation.

Industrial chemical reactions also use large amounts of energy. That energy helps make raw materials like iron and aluminum. More energy is then needed to turn those materials into products such as cars, skyscrapers, and bridges.

Most energy used by humans comes from the sun. Every day, the sun sends Earth almost 10,000 times more energy than the world needs for that day. The challenge is to capture and store solar energy so it can drive chemical processes that are useful, convenient, and nonpolluting.

Plants and many bacteria capture solar energy through photosynthesis. Humans release stored energy by burning wood, coal, petroleum, or plant products such as ethanol. They also use this energy directly when they eat food that comes from plants.

Thermochemistry is the study of heat absorbed or released during chemical and physical changes. It is used to measure the energy content of foods and to study the energetics of living organisms, such as the breakdown of sugar into carbon dioxide and water. It also supports work in the oil, gas, transportation, and renewable energy industries, as well as in engineering.

Energy is the capacity to supply heat or do work. Work means causing matter to move against an opposing force, such as when air is pushed into a bicycle tire. Energy can be described as potential energy, which depends on position, composition, or condition, and kinetic energy, which depends on motion.

A waterfall or dam stores potential energy because of its position. When the water flows downward through generators, it has kinetic energy that can do work and produce electricity in a hydroelectric plant. A battery also stores potential energy because the chemicals inside it can produce electricity when needed.

How Energy Changes in Chemical Reactions

energy basics

Chemical reactions change matter and energy at the same time. A match lighting is a simple example. These energy changes are part of everyday life and appear in food, fuels, and industry. Food provides energy through metabolic reactions. The macronutrients in food break down and help keep the body functioning. Fuels such as gasoline, natural gas, and coal are burned to produce energy for transportation, heating, and electricity generation. Industrial chemical reactions also use large amounts...

first law of thermodynamics

Energy Conservation and Internal Energy

Energy conservation describes how energy changes form during chemical and physical changes. Energy can be converted from one form into another, but the energy present before a change still exists in some form after the change is complete. This is the law of conservation of energy. It says energy can neither be created nor destroyed. The law of conservation of matter also applies during chemical change. In most chemical reactions, the total amount of matter does not show a detectable change.

internal energy

Internal Energy, Heat, and Work

Internal energy is the total of all possible kinds of energy in a substance. It is often written as U, and sometimes as E. For a system that changes energy, the important value is the change in internal energy, or ΔU. ΔU is the difference between the final internal energy and the initial internal energy. The exact values of U final and U initial are usually not known, but the first law of thermodynamics only requires ΔU. A positive ΔU means the system gained energy from the surroundings. A...

quantifying heat

Heat Transfer and Specific Heat

Heat transfer and specific heat explain how thermal energy moves and how materials respond to it. Thermal energy is the kinetic energy linked to the random motion of atoms and molecules. Temperature is a measure of how hot or cold a substance is, and it depends on how much thermal energy those particles have. When atoms and molecules move or vibrate faster, their average kinetic energy is higher. That means the object has more thermal energy and a higher temperature. When they move more...

quantifying work

Pressure-Volume Work in Chemistry

Pressure-volume work shows how gas volume changes can transfer energy in chemistry. As a system changes, its internal energy may change too. Energy can move between the system and the surroundings through heat and work. Internal energy, heat, and work are related by an energy equation. Heat depends on a measured temperature change. Work depends on a measured change in volume called pressure-volume work. Work can be defined as a force acting through a distance. Pressure-volume work, also...

enthalpy

Enthalpy and Heat at Constant Pressure

Enthalpy describes heat changes in chemical and physical processes. Chemists use the symbol H for enthalpy. It is defined as a system’s internal energy, E, plus the product of pressure, P, and volume, V. Enthalpy is a state function, so only changes in enthalpy can be measured, not the enthalpy of a substance by itself. For many reactions, the pressure stays constant. Under those conditions, the enthalpy change, ΔH, can be written in a way that includes pressure-volume work. The term PΔV...

thermochemical equations

Heat Changes in Chemical Equations

Heat changes in chemical equations show how much energy a reaction releases or absorbs. At constant pressure, the enthalpy of reaction, or ΔHrxn, is equal to the heat exchanged with the surroundings, qp. Because this value depends on how much reactant takes part, it is an extensive property. The size and sign of ΔHrxn also depend on the reaction itself and on the physical states of the substances involved. An exothermic reaction has a negative ΔHrxn value, while an endothermic reaction has a...

constant pressure calorimetry

Coffee Cup Calorimeter Heat Changes

Coffee cup calorimetry measures heat changes in reactions and physical changes using an insulated calorimeter. The calorimeter is calibrated and designed to limit heat exchange with the outside environment. That makes it possible to measure the heat taken in or released by a substance more accurately, including the energy content of foods. In calorimetry, the system is the substance or substances undergoing change. The surroundings are everything else inside the calorimeter, including the...

constant volume calorimetry

Bomb Calorimeter Heat Measurement

Bomb calorimetry measures the heat released by reactions that produce a lot of energy, especially combustion reactions. A coffee cup calorimeter works at constant pressure and is useful for reactions in solution. A bomb calorimeter works at constant volume and is used for reactions that make large amounts of heat and gaseous products. The word "bomb" refers to the strong, explosive force some reactions can have. In a bomb calorimeter, the volume does not change, so 94V = 0. That means the...

hess's law

Calculating Reaction Heat with Hess's Law

Calculating reaction heat with Hess's law lets chemists find enthalpy changes without measuring every reaction directly. Some reactions are hard or impossible to test in the lab. Even when a reaction can be measured, it is often easier to calculate the heat change from other known enthalpy values. Hess's law says that if a process can be written as the sum of several stepwise processes, the enthalpy change for the total process equals the sum of the enthalpy changes for the steps. This works...

standard enthalpy of formation

Using Standard Enthalpy Values in Chemistry

Enthalpy changes are often listed for reactions that start and end under the same conditions. Chemists use a standard state as a reference set of conditions for comparing properties. In IUPAC terms, the standard state means 1 bar of pressure and 1 M solutions, but it does not set a temperature. Many thermochemical tables still use 1 atm as the reference pressure. Because the difference between 1 bar and 1 atm is very small, enthalpy change usually stays almost the same. A superscripted o in...

enthalpies of reaction

Calculating reaction heat with Hess's law uses standard enthalpies of formation to find the enthalpy change of a reaction. When the formation values for the reactants and products are known, the overall reaction can be broken into simpler stepwise reactions. This approach helps show how the heat change for the full reaction is built from smaller parts. First, the reactants are thought of as being decomposed into their component elements. The enthalpy change for this step is proportional to the...

key terms and concepts

Explore how chemical reactions change energy in food, fuels, photosynthesis, thermochemistry, and batteries. Built for high school science learners.

How Energy Changes in Chemical Reactions | JoVE K12

chemistry

JoVE Core Chemistry brings general chemistry concepts to life using concise and easy-to-understand animated video lessons. Plus, in the scientist-in-action videos, we demonstrate classical and original research experiments performed in today's laboratories worldwide.

Matter and its Interactions

PS.Chm.4.1

Earth and Environmental Science

Earth's Systems

ESS.EES.3.2

Physical Science

PS.PSc.7.1

Pennsylvania State Academic Standards

3.2.9-12.O

3.2.9-12.P

3.2.9-12.Q

3.2.9-12.R

Louisiana Student Standards for Science

High School

Matter And Its Interactions

HS-PS1-4

HS-PS1-5

HS-PS3-2

HS-PS3-3

HS-PS3-4

Physics

HS-PS3-1

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Study Of Matter

Classification of matter

Energy And Waves

Thermal energy

Interactions Of Matter

Chemical reactions

Physical Geology

Earth's Resources

Energy resources

Tennessee Academic Standards

CHEM1.PS3.3

Virginia  Standards of Learning

HIgh School

CH.7

CH.7.a

Earth Science

ES.6

ES.6.d

Minnesota Academic Standards in Science

3.1.1 9C.2.2.1.1

Texas Essential Knowledge and Skills

CHEM.13

CHEM.13.A

CHEM.13.C

Alabama Course of Study Science

9-12.PS.1.1

Earth and Space Science

Earth's Place in the Universe

9-12.ESS.1.1

9-12.ESS.1.1.a

Next Generation Science Standards

Life Science

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

HS-LS1-7

Florida Department of Education

SC.912.E.6

SC.912.E.6.6

SC.912.P.10

SC.912.P.10.1

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

Matter and Its Interactions

C-PS1-4

C-PS1-5

C-PS3-4

P-PS3-1

P-PS3-2

P-PS3-3

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Energy

HS-PS3-1.

Georgia Standards of Excellence

SPS7.

Types of Energy

Classifying Matter by State

Chemistry is the study of matter and the changes it undergoes. Matter is anything that has mass and occupies space. Matter is all around us; the air, ...

Classifying Matter by Composition

Matter: Pure Substances and Mixtures
According to its composition, the matter can be classified into two broad categories &mdash; pure substances and ...

physical-and-chemical-properties-of-matter

Physical and Chemical Properties of Matter

The characteristics that enable us to distinguish one substance from another are called properties.

Physical Properties of Matter

A physical property is ...

molecular-comparison-of-gases-liquids-and-solids

Molecular Comparison of Gases, Liquids, and Solids

Particles in a solid are tightly packed together (fixed shape) and often arranged in a regular pattern; in a liquid, they are close together with no ...

Intermolecular vs Intramolecular Forces

Intermolecular forces (IMF) are electrostatic attractions arising from charge-charge interactions between molecules. The strength of the intermolecular ...

Intermolecular Forces

Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions ...

comparing-intermolecular-forces-melting-point-boiling-point

Comparing Intermolecular Forces: Melting Point, Boiling Point, and Miscibility

Intermolecular forces are attractive forces that exist between molecules. They dictate several bulk properties, such as melting points, boiling points, ...

surface-tension-capillary-action-and-viscosity

Surface Tension, Capillary Action, and Viscosity

Surface Tension
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded ...

States of Matter and Phase Changes

The internal energy of a substance&#8212;the total kinetic energy of all its molecules and the potential energy of their associated forces&#8212;depends ...

Phase Transitions

Whether solid, liquid, or gas, a substance&#39;s state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the ...

phase-transitions-vaporization-and-condensation

Phase Transitions: Vaporization and Condensation

The physical form of a substance changes on changing its temperature. For example, raising the temperature of a liquid causes the liquid to vaporize ...

Vapor Pressure

When a liquid vaporizes in a closed container, gas molecules cannot escape. As these gas phase molecules move randomly about, they will occasionally ...

Clausius-Clapeyron Equation

The equilibrium between a liquid and its vapor depends on the temperature of the system; a rise in temperature causes a corresponding rise in the vapor ...

Phase Transitions: Melting and Freezing

Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy ...

phase-transitions-sublimation-and-deposition

Phase Transitions: Sublimation and Deposition

Some solids can transition directly into the gaseous state, bypassing the liquid state, via a process known as sublimation. At room temperature and ...

Heating and Cooling Curves

When a substance&#8212;isolated from its environment&#8212;is subjected to heat changes, corresponding changes in temperature and phase of the substance ...

Phase Diagrams

A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance. ...

Use models to explain how changes in energy affect the arrangement and movement of the particles in solids, liquids, and gases, as well as the relative strengths of their intermolecular forces.

PS.Chm.7.1

Chemical reactions, such as those that occur when you light a match, involve changes in energy as well as matter.

Chemical changes and their accompanying ...

First Law of Thermodynamics

Energy Conservation

Energy can be converted from one form into another, but all of the energy present before a change occurs always exists in some form ...

Internal Energy

The total of all possible kinds of energy present in a substance is called the internal energy (U), sometimes symbolized as E. Suppose a system with ...

Quantifying Heat

Thermal Energy&#160;

Microscopically, thermal energy is the kinetic energy associated with the random motion of atoms and molecules. Temperature is a ...

Quantifying Work

As a system undergoes a change, its internal energy can change, and energy can be transferred from the system to the surroundings, or from the ...

Enthalpy

Chemists ordinarily use a property known as enthalpy (H) to describe the thermodynamics of chemical and physical processes. Enthalpy is defined as the sum ...

Thermochemical Equations

For a chemical reaction (the system) carried out at constant pressure &ndash; with the only work done caused by expansion or contraction &ndash; the ...

Constant Pressure Calorimetry

Calorimetry is a technique used to measure the amount of heat involved in a chemical or physical process or to measure the heat transferred to or from a ...

Constant Volume Calorimetry

Calorimeters are useful to determine the heat released or absorbed by a chemical reaction. Coffee cup calorimeters are designed to operate at constant ...

Use mathematics and computational thinking to execute simple calorimetric calculations based on the Law of Conservation of Energy.

Understand the relationship among pressure, temperature, volume, and phase.

How Energy Changes in Chemical Reactions

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